Flow diverters are medical devices designed to treat intracranial aneurysms, which are weakened, bulging areas in brain blood vessels. These devices work by redirecting blood flow away from the aneurysm, promoting its natural healing. This approach represents a minimally invasive, endovascular technique for managing these complex vascular conditions.
Understanding Intracranial Aneurysms
An intracranial aneurysm is a balloon-like bulge that forms on a blood vessel in the brain. This weakening of the vessel wall can occur due to various factors, including genetic predisposition, high blood pressure, or atherosclerosis. The primary danger associated with an aneurysm is its potential to rupture, leading to a subarachnoid hemorrhage, a type of bleeding in the brain that can cause severe neurological damage or be life-threatening.
Traditional treatments for intracranial aneurysms include surgical clipping and endovascular coiling. Surgical clipping involves opening the skull to place a small metal clip at the base, or neck, of the aneurysm, effectively sealing it off from the blood flow. Endovascular coiling, a less invasive procedure, involves filling the aneurysm sac with tiny platinum coils inserted through a catheter, which promotes clotting within the aneurysm. These methods have limitations, especially for aneurysms with wide necks or those that are large or irregularly shaped, making complete and stable occlusion challenging.
The parent artery is the main blood vessel from which the aneurysm originates, and the aneurysm neck is the junction where the aneurysm connects to this main artery. Aneurysms with wide necks pose a particular challenge for coiling because coils might protrude into the parent artery, potentially leading to blood clots or incomplete occlusion. This highlights the need for alternative treatment strategies like flow diversion.
Mechanism of Flow Diversion
A flow diverter is a specialized endovascular prosthesis, essentially a braided mesh tube. Its high metal coverage is important for its function. It is positioned within the parent artery, directly across the aneurysm neck, rather than inside the aneurysm sac itself.
The design of the flow diverter works by significantly reducing the amount of blood flow entering the aneurysm sac. By diverting the blood away, the stagnant blood within the aneurysm begins to clot, a process known as thrombosis. Over time, the body’s natural healing mechanisms are stimulated.
New tissue, called endothelium, starts to grow across the surface of the flow diverter at the aneurysm neck. This tissue growth seals off the aneurysm from the main blood vessel, reconstructing the parent artery and allowing it to heal. This gradual process leads to the complete occlusion and shrinkage of the aneurysm.
The Flow Diverter Procedure
The flow diverter procedure is performed under general anesthesia. It begins with the insertion of a catheter into an artery, often in the groin or wrist. This catheter is then guided through blood vessels up to the brain, using imaging to navigate the vascular system.
Prior to the procedure, patients are prescribed dual antiplatelet therapy, such as aspirin and clopidogrel. This therapy prevents blood clots from forming on the newly implanted device and within blood vessels. This regimen begins several days before the procedure and continues for a period afterward.
Once the catheter is in position, the flow diverter device is deployed across the aneurysm neck. The surgeon withdraws the catheter, ensuring the device is correctly positioned. Patients remain in the hospital for a few days for monitoring, though some return home the day after.
Expected Outcomes and Potential Risks
Flow diverters have shown high rates of aneurysm occlusion. This healing process is gradual and can take several months, with complete closure often occurring around six months after the procedure. Some studies indicate complete occlusion rates of over 80% across various aneurysm types.
Potential risks and complications associated with flow diversion include hemorrhage and ischemic stroke. These can occur due to factors like thromboembolism or blockage of small vessels. Neurological complications and mortality rates have been reported, with some studies indicating permanent morbidity between 1.4% and 7.6% and mortality between 4% and 8%.
Risks can also relate to the antiplatelet therapy, such as increased bleeding. Patient selection is important for outcomes. Regular follow-up imaging, such as angiograms or CTA, is performed at regular intervals to monitor the aneurysm’s healing and the device’s patency.